Ni0.8Mn0.2Cr0.5Fe1.5-xGdxO4 (where x=0, 0.02, 0.04, 0.06, 0.08) spinel ferrites were synthesized by a sol–gel autocombustion technique using citric acid as fuel. Effect of Gd doping on structural and ...magnetic properties of Ni–Mn–Cr ferrites is reported. The phase composition of the prepared samples was analyzed by X-ray diffraction and Fourier transform infrared spectroscopy, and the magnetic measurements were realized using a vibrating sample magnetometer. XRD and FT-IR analysis reveal pure spinel phase in all the samples, without traces of secondary phases. The grain sizes were estimated from the TEM micrographs and were found to decrease with the doping ions concentration from 43 to 10nm. It was revealed from the hysteresis loop of the materials that magnetization and coercivity followed decreasing trend with substitution of Fe3+ magnetic ions by Gd3+ ions. Also, introducing Gd ions into the spinel lattice led to the decrease in Curie temperature.
•Gd doped Ni–Mn–Cr ferrites were obtained using the sol–gel autocombustion technique.•XRD and IR analysis reveals the pure spinel structure.•Average grain size decrease with Gd-content.•Saturation magnetization, coercivity and Curie temperature decrease with Gd doping.
A series of silicone–barium titanate composites (multiple specimens of each sample), designed as dielectric elastomeric films to be used as active elements in wave energy conversion devices, were ...immersed in artificial sea water in pseudo-dynamic conditions. While some of specimens were extracted after half a year and subsequently subjected to UV irradiation for 500 h (ASW1/2 + UV procedure), the rest were kept in the saline environment for one year (ASW procedure). The changes that occurred in the structure and morphology as well as in mechanical and dielectric properties were assessed by comparing the obtained results to those of the original samples. Thus, the surface and cross-section morphology was studied by Scanning Electron Microscopy (SEM) having an attached Energy Dispersive X-ray system (EDX), which was used for qualitative elemental analysis and elemental mapping. Changes in surface roughness due to the aging of samples were estimated on the basis of Atomic Force Microscopy (AFM) measurements. The thermal transitions were identified from the Differential Scanning Calorimetry (DSC) data and based on these, the crystallinity degree of the samples was evaluated in each of the three stages. The changes in the structural order were also verified by Wide Angle X-ray Diffraction (WAXD). The tensile toughness, as the amount of energy per volume unit that the material can absorb until failure, was estimated by the area under tensile stress–strain curves. The toughness at 100% elongation was determined on the basis of cyclic stress–strain curves of the original samples as an indirect measure of the energy that the elastic material could release when force that acted on it is removed, like in an energy harvesting system. The aging effect on the viscoelasticity of the samples was evaluated by dynamic mechanical analysis (DMTA), while dielectric spectroscopy was used to estimate the changes in dielectric properties.
A new polymer-inorganic nanocomposite composed of fibrous Na–Mg triple chain hydrosilicate with a poly(amide-imide) matrix was developed. Its structure, morphology, and dynamic mechanical properties ...were studied. Stability and high values of mechanical characteristics were shown in a wide temperature range from –150 to 300°C for both the polymer and a composite based on it. The introduction of the fibrous hydrosilicate nanofiller led to a structuring of the polymer matrix and a change from an amorphous state to an ordered mesomorphic state. A comparative analysis of the free and cryo-fracture surface morphologies of the polymer films and composites was carried out. A model of the structure of the polymer matrix with a network of hydrogen bonds, the density of which depends on the reduced viscosity of the casting solution, was proposed.
Organic-coated iron-chromium oxide (chromite) nanoparticles have been prepared by using the thermal decomposition procedure. For this purpose, the substrate - bimetallic acetate - was treated with ...oleic acid and dodecylamine as co-ligands in trichloroacetic acid solvent at high temperature (320 degree C). The main characteristics and behaviors of the obtained nanoparticles were investigated by combined techniques. The size of the obtained nanoparticles was around 11 nm, as estimated by TEM, WAXD and SAXS, which were in good agreement. The bimetallic nature of the nanoparticles was emphasized by X-ray energy dispersive spectrometry (EDX) and their structure was confirmed by WAXD. The Fourier transform infrared (FTIR) spectrum revealed the bands characteristic to metal oxides as well as to the organic components and confirmed the replacement of the acetate with long chain ligands. The co-existence of the organic coatings and metallic core induced a special behavior that was studied by thermogravimetric analysis, differential scanning calorimetry and polarized optical microscopy. The coated bimetallic nanoparticles proved to be thermostable up to 252 degree C and thermotropic showing a highly organized crystalline smectic mesophase (3D plastic mesophase). The organic part alone, in the absence of the inorganic component, did not develop this self-assembly. The results of the magnetic measurements suggest superparamagnetic behavior of the iron-chromium oxide nanoparticles and a weak ferromagnetic behavior.
New polydimethylsiloxane-containing segmented block copolyurethanes were obtained from aromatic or aliphatic diisocyanates, 1,4-butanediol and poly(ethylene glycol)adipate using a multistep ...polyaddition process. The polydimethylsiloxane–polyurethane elastomers were characterized by IR and NMR spectroscopy, DSC, WAXD and TEM measurements. Transmission electron microscopy showed that the polydimethylsiloxane contains spherulites uniformly dispersed in the continuous amorphous poly(ether urethane) matrix.
4-Azidodiphenyl was photolysed with low intensity radiation in oxygen-free and oxygen containing dichloromethane solutions. It was found that the main product is azodiphenyl when the concentration is ...greater than about 10
−2
mol/l and oxygen is absent. In the case of oxygen containing diluted azide solutions, the triplet azide molecules are trapped by oxygen to form, probably, a nitroazodiphenyl intermediate. In both cases, the light-induced decomposition of azide can be treated approximately as a unidirectional first order (UFO) reaction, where the reactant is the only light absorbent. The deviation from such kinetics appearing at high azide conversions is mainly caused by the nitrene—solvent reaction. The concentration of unreacted azide was measured by the absorbance at 276
nm.
New bismaleimides containing ether groups in the backbone were synthesized and characterized. They were prepared by reacting maleic anhydride with various diamines (having ether groups). Monomers ...were characterized by infrared and proton nuclear resonance spectroscopy as well as by elemental analysis. The thermal properties of the bismaleimides were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), differential thermogravimetry (DTG) and isothermal gravimetric analysis (IGA).
New hybrid materials have been prepared by sol-gel technique. They have been obtained from bismaleimide monomers either in reaction with N-(3-triethoxysilylpropyl)furan-2-carboxamide monomer, by a ...Diels-Alder reaction, or in reaction with (3-aminopropyl)triethoxysilane following a Michael addition reaction. The sol-gel process was conducted with or without adding different amounts of tetraethyl orthosilicate. The structures of the obtained compounds have been confirmed by proton nuclear magnetic resonance and Fourier transform infrared spectroscopy. A comparative study between Diels-Alder- and Michael addition-type products regarding their thermal and mechanical properties was also conducted for samples as obtained from synthesis. The thermoreversible character of the Diels-Alder hybrid materials has been demonstrated with the aids of differential scanning calorimetry and attenuated total reflectance Fourier transform infrared spectroscopy, the results from both methods being in good agreement with each other, and with literature data. The morphology of hybrid materials was studied by the atomic force microscopy, optical microscopy for three different stages: initial (24°C), at heating (150°C), and after cooling at 24°C, and scanning electron microscopy. All data confirmed the driving force for the dispersion of the Si-containing aggregates in the Michael addition series is the dynamic evolution of the sol-gel process, whereas the Diels-Alder series behavior is ruled by the thermoreversible character of the Diels-Alder cycloaddition.
Polydimethylsiloxane-α,ω-diol was used as matrix for the preparation of polysiloxane-SiO2-TiO2 composites through in situ incorporation of silica and titania using a solvent-free sol-gel procedure. ...For this purpose, oxide precursors tetraethyl-orthosilicate and tetrabutyl-orthotitanate, and a proper condensation catalyst, viz. dibuthyltin dilaurate, were added in pre-established amounts to the polymer. The hydrolysis and condensation reactions take place under mild conditions, with the formation of silicon and titanium oxide networks and polymer crosslinking. The effect of SiO2 and TiO2 mass ratio on the morphology of the composites was investigated by scanning electron microscopy (SEM) and X-rays diffraction (XRD), and interpreted in correlation with differential scanning calorimetry (DSC) and energy-dispersive X-ray spectroscopy (EDX) data. The film samples were tested as active elements in actuation devices.
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